The present invention relates to an image-pickup apparatus such as a video camera and a digital still camera.
Autofocus (AF) control methods for image-pickup apparatuses include a so-called TV-AF method which generates an AF evaluation value signal using high-frequency components (contrast components) extracted from an image (video) signal and searches for a focus lens position (in-focus position) where the AF evaluation value signal is at the maximum.
Further, a so-called hybrid AF method has been proposed in which the TV-AF method and an external ranging AF method or an internal phase difference AF method are combined (see Japanese Patent Laid-Open No. 2002-258147). The external ranging AF method measures a distance to an object to control a focus lens, and the internal phase difference AF method measures a defocus amount of an image-pickup optical system to control a focus lens.
The hybrid AF method moves the focus lens to the vicinity of the in-focus position using ranging information or phase difference information and then moves the focus lens therefrom by the TV-AF method, thereby achieving an in-focus state with high focusing accuracy in a short time.
In such a hybrid AF method using the external ranging AF method, a distance sensor is placed independently from the image-pickup optical system. The distance sensor has a high degree of freedom in layout in the image-pickup apparatus, which is advantageous to reduce the size of the image-pickup apparatus.
However, when an accessory device such as a conversion lens is attached to the image-pickup apparatus equipped with the distance sensor, light traveling from an object toward the distance sensor may be blocked by the accessory device. This makes an accurate calculation of the object distance with the distance sensor impossible.
In other words, a large difference is generated between an in-focus position according to the object distance acquired by the distance sensor and an accurate in-focus position acquired by the TV-AF method.
In such a situation, the focus lens is once moved to a position away from the accurate in-focus position, and then it is moved so as to search for the in-focus position by the TV-AF method.
This causes the image-pickup optical system to focus on an object other than the desired object or makes the time until achieving an in-focus state longer. In particular, the longer time until achieving an in-focus state causes a video camera to pick up an out-of-focus video for a longer time.
Therefore, it is necessary to cause the image-pickup apparatus to recognize whether or not an output from a light-receiving sensor used for the AF control, such as a distance sensor, is influenced by the attachment of the accessory device.